1. Technical Field
The present invention relates to an illumination device, such as a backlight unit used for a liquid crystal display of a cellular phone, and to an optical waveguide for the same.
2. Related Art
In liquid crystal display devices, a backlight unit is provided on a rear surface of a liquid crystal display panel in order to perform transmissive display. Generally, the backlight unit is composed of an illumination device which includes alight source, an optical waveguide for radiating light emitted from the light source onto a rear surface of the liquid crystal display panel as planar light, a diffusion sheet for diffusing the light emitted from the optical waveguide, and a prism sheet for condensing the light.
As a cellular phone in which a liquid crystal display device is used for a display unit, a cellular phone of a double-sided panel type has been known in which a main body has a large main display panel provided at an inner surface side of a foldable display unit and a small sub-display panel provided at a rear surface side. In contrast, in recent years, a slide-type cellular phone or a rotation-type cellular phone has been on sale. The slide-type cellular phone has a structure in which a display unit is mounted on a main body unit so as to be separate from the main body and the rotation-type cellular phone has a structure in which a main display panel normally located at an inner surface side is reversible so as to be exposed to the outside. Generally, these cellular phones mostly have a structure in which only one large main display panel is provided without a sub-display panel and the main display panel serves as the sub-display panel.
However, in the above-mentioned slide-type or rotation-type cellular phone, simple display information, such as the time and remaining battery level displayed on the sub-display panel in the case of a double-sided type is also displayed on the one main display panel. For this reason, even though the simple display information can be confirmed, it is necessary that the entire liquid crystal display panel be illuminated whenever the display information is confirmed, which results in an increase in consumed power.
In addition, as an example of the illumination device used for liquid crystal display devices, Japanese Unexamined Patent Application Publication No. 2001-281655 discloses an illumination device in which a reflective surface of an optical waveguide is a curved surface having an optical focus and which becomes a surface light source that has low power consumption and low luminance brightness in order to be used for a backlight of the liquid crystal display panel.